Method for making electrode of polymer composite

ABSTRACT

This invention provides a method for making an electrode film for a composite polymer material. A composite plating method is used to form a conductive plate film with microrough surface of 0.01 to 100 microns which will be adhered to a composite polymer material, enhances the adhering performance and reduces the interface electrical resistance.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention generally relates to a method for making aconductive electrode for a composite polymer material, and moreparticularly, relates to a method for making a metallic electrode onwhich a microrough surface is formed by a composite plating process.

2. Related Art

For the demands of electrical conductivity, abrasion resistance andwiring with other metal elements, a conductive polymer composite isgenerally coated with a metallic film so as to be made into a reactiveelement, such as a capacitor or a resistor.

Due to the different coefficients of expansion for the metallicelectrode and the conductive polymer, poor contact between the twogenerally occur. A first problem is that when the polymer composites areapplied to resistors or components of positive temperature coefficient,the poor contact between the metallic electrode and the conductivepolymer becomes more critical since they encounter cyclic or non-cyclictemperature variances. The second problem concerns with the resistanceof interface between the metallic electrode and the conductive polymer.Since the conductive polymer is made from conductive grains andinsulating polymer material, during the adhering process of the metallicelectrode to the conductive polymer, the insulating polymer material mayflow into the interface of the conductive grains and the metallicelectrode, causes higher resistance and decreases the performance of thefinished polymer composite.

FIGS. 1a to 1 c are sectional views showing the interface of theconductive polymer 10 and the metallic electrode 12 in three stages ofenlargement. The views clearly show that the contact surfaces of thepolymer 10 and the metallic electrode 12 are smooth.

To solve the problems of poor contact and higher interface resistance,U.S. Pat. Nos. 4,689,475 and 4,800,253 disclose compositions of metallicelectrode and conductive polymer element in which the metallic electrodehas a microrough surface, for example, having irregularities whichprotrude from the surface with a height of 0.1 to 100 microns, toimprove its adhesion to the conductive polymer. As shown in FIGS. 2a to2 c, the three stage enlarged sectional views of the interface of theconductive polymer 10 and the metallic electrode 14, the microroughsurface of the metallic electrode 14 will improve the adhesive strengthof the electrode 14 to the polymer 10, and enhance the conductivity ofthe electrode 14 and the conductive polymer 10 by the larger contactarea of the microrough surface. But, the processes for forming themicrorough surfaces are not disclosed in the two patents, and theroughness of the electrode 14 is not enough. In the U.S. Pat. No.4,689,475, the metallic electrode 14 and the polymer 10 contact only byimpacting. The U.S. Pat. No. 4,800,253, which is a continuation-in-partof U.S. Pat. No. 4,689,475, makes the electrode in direct physicalcontact with the conductive polymer element and having two-stageprotrusions which may enhance the connection of the electrode and thepolymer. But, during impacting, there is no excess cavity for thepolymer composite to flow, as a result, the insulating polymer materialflowing into the interface of the conductive grains and the metallicelectrode still decreases the conductivity of the electrode and thepolymer.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide aconductive film, having microrough surface made by a composite platingmethod, to be applicable as an electrode of a polymer composite, so thatthe conductive polymer composite performs higher adhesive strengthbetween the electrode and the polymer, and lower interface resistancetherebetween.

In order to achieve the foregoing objective, the present inventionprovides a method for making a conductive polymer composite. The methodincludes the following steps: providing a conductive polymer basematerial; utilizing a composite plating method to form an electrodehaving microrough surface of layer, measured 0.1 to 100 microns, on asurface of a base material; and finally pressing the electrode onto theconductive polymer base material. The microrough electrode made bycomposite plating method enhances the adhering strength of the electrodeto the polymer composite, and provides suitable cavities for the flow ofpolymer so as to prevent the insulating polymer from filling into theclearance between the electrode and the conductive grains, and ensuresthe lower interface resistance.

Another objective of the present invention is to provide a process forfabricating composite plating films which have microrough surfaces. Theprocess includes the following steps: preparing a plating tankcontaining a metal plating solution and insoluble particles dispersed inthe metal plating solution; placing a polymer base material on thecathode while placing a metal on the anode of a power supply for platingand forming a microrough surface of 0.1 to 100 microns roughness on thebase material.

A further objective of the present invention is to provide an electronicelement including a conductive polymer base material and a conductiveelectrode having microrough surface of 0.1 to 100 microns in roughness.The microrough surface of the electrode can firmly adhere to thecomposite polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, together with the objects and advantages thereof,may best be understood by reference to the following description of thepreferred embodiments taken in conjunction with the accompanyingdrawings in which:

FIGS. 1a to 1 c are sectional views showing the interface of a prior artconductive polymer element and a metallic electrode in three stages ofenlargement;

FIGS. 2a to 2 c are sectional views showing the interface of anotherprior art conductive polymer element and a metallic electrode in threestages of enlargement; and

FIGS. 3a to 3 c are sectional views showing the interface of aconductive polymer element and a metallic electrode according to thepresent invention in three stages of enlargement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Composite plating is presently used to make surfaces finishing for thefunctions of abrasion resistance, hardness enhancement orheat-resistance reducing. The insoluble particles added in the platingsolution are chosen from one of silicon carbide (SiC), aluminum oxide(Al₂O₃), tungsten carbide (WC), chromium oxide (Cr₂O₃), diamond andgraphite, as disclosed in U.S. Pat. Nos. 5,651,872 and 5,282,536. Thepresent invention utilizes the composite plating method by selectingsuitable insoluble particles and the particle size thereof to form asuitable microrough surface on the metallic electrode and solve theproblems of adhering strength and interface electrical resistance whenthe electrode is adhered onto the conductive polymer.

The process for fabricating a composite plating film by the compositeplating method is described below.

1) preparing a base material, such as electrical conductive glass,stainless steel, nickel foil or copper foil, as a receiver for theplating film to form on during the proceeding plating process;

2) removing oil or impurities from the surfaces of the base material;

3) plating by first preparing the composite plating solution of metalplating solution and insoluble particles. The metal plating solution ischosen from nickel plating solution, copper plating solution, nickelalloy solution or copper alloy solution. The insoluble particles arechosen from at least one of carbon black, graphite, nickel powder,nickel-plated graphite powder, copper powder, copper-plated graphitepowder or others. Then, placing an electrode metal on the anode of theplating tank, placing the base material on the cathode, and applyingelectric current to conduct plating;

4) cleaning the conductive film, which is disposed on the base materialafter plating, to clean up the impurities on the film;

5) peeling off the conductive film from the base material. But, if thebase material, e.g., copper foil, is capable of being used as anelectrode, the base material with the film can be directly used; and

6) drying the conductive film or also the base material for furtherprocess of making into electrode.

Besides, for dispersing the insoluble particles evenly in the platingsolution and ensuring uniform roughness of the plate film, the compositeplating solution has to be processed by the following steps:

a) gradually adding the insoluble particles into the plating solution;

b) separating the insoluble particles by ultrasonic wave; and

c) circulating and stirring the composite plating solution.

In the aforesaid composite plating process, the materials and processconditions should be suitably accommodated in order to obtain thedesired roughness of the plate film. For example, if nickel platingsolution is taken, the concentration of the nickel solution is 10 to 200g/l, and preferably 40 to 100 g/l; if copper plating solution is taken,the concentration of the copper solution is same of 10 to 200 g/l, andpreferably 40 to 100 g/l. The concentration of the insoluble particlesis 1 to 30 g/l, and the average size thereof is 0.01 to 100 microns. Thecurrent density of plating is controlled within 0.5 to 10 ASD, andpreferably within 2 to 6 ASD. The temperature is controlled within roomtemperature (25 degree centigrade) to 60 degree centigrade, andpreferably within 35 to 55 degree centigrade.

By the aforesaid plating process, at least a microrough surface of 0.01to 100 microns can be formed on the plate film. As shown in FIGS. 3a to3 c, two electrodes 16 made from composite plate films are placed onboth sides of a conductive polymer element 10. The electrodes 16 and theconductive polymer 10 are then hot-pressed to adhere. The material ofthe electrodes 16 are chosen from alloys of nickel, nickel-cobalt,nickel-ferrum, nickel-manganese, nickel-zinc, nickel-phosphorus,nickel-boron, and nickel-palladium, etc., in which the volume percentageof nickel is more than 70%; or the material of the electrodes 16 can bechosen from alloys of copper, copper-zinc, and copper-nickel, etc., inwhich the volume percentage of copper is more than 70% also.

As described above, the surface of the electrode made from compositeplating can be formed with suitable roughness, which not only enhancesthe adhering strength of the electrode to the polymer composite; butalso provides suitable cavity for the insulating polymer to flow andprevents the insulating polymer to flow into the clearance of conductivegrains and the electrode so as to ensure the lower resistance.

The following examples are composite polymer products made fromdifferent raw materials and verified through thermo cycling tests toprove their quality.

The conditions of thermo cycling test are: exposing the finishedelectrode composite polymer under circulating hot air of 100 degreecentigrade for 30 minutes, then naturally cooling it in the room air for15 minutes; and repeating the procedures for at least 100 cycles. Thetest piece is viewed by eyes if there is any separation or deformationbetween the electrode and the polymer.

The test pieces are made as follows.

1) mixing and extruding conductive composite polymer grains by abi-screw extruder made by WP Co. (ZSK 25). The compositions of highdensity polyethylene (HDPE) and carbon black are as follows:

Weight Composition Commercial Name Percentage Manufacturer HDPE LH-60670% Taiwan Polymer Carbon black XC-71 30% Cabot, US

2) heat-molding the polymer grains under 160 degree centigrade to formcircular test pieces of 65.0 mm diameter and 1.0 mm thickness;

3) cutting conductive electrode films made by aforementioned compositeplating method into foils of 65.0 mm diameter; placing two foils on eachpolymer test piece; heat-pressing them under 160 degree centigrade toform into a piece, and cooling it for test use.

The composite plating is conducted as follows:

First Embodiment

Plating solution: [Ni₂ ⁺], 60 g/l;

Boric acid: 20 g/l;

pH: 4.5;

Temperature: 50 degree centigrade;

Current density: 5 ASD;

Plating time: 10 minutes; and

Insoluble particles: carbon black (XC-72, Carbot, US) or graphite withgrain size less than 1 micron, 4 g/l.

The test result is no separation or deformation.

Second Embodiment

Plating solution: [Ni₂ ⁺], 20 g/l, [Co₂ ⁺], 4 g/l;

Boric acid: 20 g/l;

pH: 4.5;

Temperature: 45 degree centigrade;

Current density: 5 ASD;

Plating time: 10 minutes; and

Insoluble particles: carbon black (Raven, Columbian Chemical, US) ornickel powder with grain size of 10 to 20 micron, 6 g/l.

The test result is no separation or deformation.

Third Embodiment

Plating solution: [Cu₂ ⁺], 30 g/l;

Amine sulphate: 25 g/l;

pH: 4.5;

Temperature: 45 degree centigrade;

Current density: 7 ASD;

Plating time: 5 minutes; and

Insoluble particles: carbon black (XC-72, Carbot, US) or graphite withgrain size less than 1 micron, 4 g/l.

The test result is no separation or deformation.

Although the present invention has been described in detail withreference to its presently preferred embodiments, it should beunderstood by those skilled in the art that various modification andvariations can be made without departing from the spirit or scope of thepresent invention. Therefore, the present embodiment is to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope of the appended claims.

What is claimed is:
 1. A method for making a conductive polymercomposite having an electrode, comprising the steps of: providing aconductive polymer element; utilizing a composite plating method to forman electrode film having a microrough surface on a conductive base; andpressing the electrode onto the conductive polymer element; wherein thecomposite plating method comprises the steps of: preparing a compositeplating solution containing a metal plating solution and insolubleparticles; placing a base material on a cathode of a plating apparatus;placing a conductive base on an anode of a plating apparatus; andconducting plating to form the microrough surface of the electrode;further wherein the composite plating solution is prepared using thefollowing steps: gradually adding the insoluble particles into theplating solution; applying ultrasonic wave to keep the insolubleparticles segregated from each other; circulating and stirring thecomposite plating solution.
 2. A method for making a conductive polymercomposite according to claim 1, wherein the roughness of the microroughsurface is about 0.1 to 100 microns.
 3. A method for making a conductivepolymer composite according to claim 1, wherein the base material ischosen from one of electrical conductive glass, stainless steel, nickelfoil, copper foil and the like.
 4. A method for making a conductivepolymer composite according to claim 1, wherein the metal platingsolution is chosen from one of nickel plating solution, copper platingsolution, nickel alloy solution, copper alloy solution and the like. 5.A method for making a conductive polymer composite according to claim 1,wherein the insoluble particles are chosen from at least one of carbonblack, graphite, nickel powder, nickel-plated graphite powder, copperpowder, copper-plated graphite powder and the like.
 6. A method formaking a conductive polymer composite according to claim 1, wherein theconcentration of the metal in the metal plating solution is 10 to 200g/l, the concentration of the insoluble particles is 1 to 30 g/l, andthe average size thereof is 0.01 to 100 microns.
 7. A method for makinga conductive polymer composite according to claim 6, wherein theconcentration of the metal in the metal plating solution is preferably40 to 100 g/l.
 8. A method for making a conductive polymer compositeaccording to claim 6, wherein the concentration of the insolubleparticles is preferably 4 to 10 g/l.
 9. A method for making a conductivepolymer composite according to claim 1, wherein the current density ofplating is controlled within 0.5 to 10 ASD, and under temperature of 25to 60 degree centigrade.
 10. A method for making a conductive polymercomposite according to claim 9, wherein the current density of platingis preferably controlled within 2 to 6 ASD.
 11. A method for making aconductive polymer composite according to claim 9, wherein thetemperature is preferably 35 to 55 degree centigrade.
 12. A method formaking a conductive polymer composite according to claim 1, wherein thematerial of the electrode is chosen from one of the alloys of nickel,nickel-cobalt, nickel-iron, nickel-manganese, nickel-zinc,nickel-phosphorus, nickel-boron, nickel-palladium, and the like.
 13. Amethod for making a conductive polymer composite according to claim 12,wherein the volume percentage of the nickel in the material of theelectrode is at least 70%.
 14. A method for making a conductive polymercomposite according to claim 1, wherein the material of the electrode ischosen from one of the alloys of copper, copper-zinc, copper-nickel, andthe like.
 15. A method for making a conductive polymer compositeaccording to claim 14, wherein the volume percentage of the copper inthe material of the electrode is at least 70%.
 16. A method for making aconductive plating film having a microrough surface, comprising thesteps of: preparing a plating tank having a composite plating solutioncontaining a metal plating solution and insoluble particles; placing abase material on a cathode of a plating apparatus; placing a conductivebase on an anode of a plating apparatus; and conducting plating to formthe microrough surface of the electrode on the base material saidmircorough having a surface roughness ranging from 0.01 to 100 microns;wherein the composite plating solution is prepared using the followingsteps: gradually adding the insoluble particles into the platingsolution; applying ultrasonic wave to keep the insoluble particlessegregated from each other; circulating and stirring the compositeplating solution.
 17. A method for making a composite plating filmhaving a microrough surface according to claim 16, wherein the basematerial is chosen from one of electrical conductive glass, stainlesssteel, nickel foil, copper foil and the like.
 18. A method for making acomposite plating film having a microrough surface according to claim16, wherein the metal plating solution is chosen from one of nickelplating solution, copper plating solution, nickel alloy solution, copperalloy solution and the like.
 19. A method for making a composite platingfilm having a microrough surface according to claim 16, wherein theinsoluble particles are chosen from at least one of carbon black,graphite, nickel powder, nickel-plated graphite powder, copper powder,copper-plated graphite powder and the like.
 20. A method for making acomposite plating film having a microrough surface according to claim16, wherein the concentration of the metal in the metal plating solutionis 10 to 200 g/l, the concentration of the insoluble particles is 1 to30 g/l, and the average size thereof is 0.01 to 100 microns.
 21. Amethod for making a composite plating film having a microrough surfaceaccording to claim 20, wherein the concentration of the metal in themetal plating solution is preferably 40 to 100 g/l.
 22. A method formaking a composite plating film having a microrough surface according toclaim 20, wherein the concentration of the insoluble particles ispreferably 4 to 10 g/l.
 23. A method for making a composite plating filmhaving a microrough surface according to claim 16, wherein the currentdensity of plating is controlled within 0.5 to 10 ASD, and undertemperature of room air to 60 degree centigrade.
 24. A method for makinga composite plating film having a microrough surface according to claim23, wherein the current density of plating is preferably controlledwithin 2 to 6 ASD.
 25. A method for making a composite plating filmhaving a microrough surface according to claim 23, wherein thetemperature is preferably 35 to 55 degree centigrade.
 26. A method formaking a composite plating film having a microrough surface according toclaim 16, wherein the material of the electrode is chosen from one ofthe alloys of nickel, nickel-cobalt, nickel-iron, nickel-manganese,nickel-zinc, nickel-phosphorus, nickel-boron, nickel-palladium, and thelike.
 27. A method for making a composite plating film having amicrorough surface according to claim 26, wherein the volume percentageof the nickel in the material of the electrode is at least 70%.
 28. Amethod for making a composite plating film having a microrough surfaceaccording to claim 16, wherein the material of the electrode is chosenfrom one of the alloys of copper, copper-zinc, copper-nickel, and thelike.
 29. A method for making a composite plating film having amicrorough surface according to claim 28, wherein the volume percentageof the copper in the material of the electrode is at least 70%.